The Systems Biology Markup Language (SBML) is an XML-based format for the exchange of quantitative and qualitative models of biochemical reaction networks. An SBML Forum meeting, the ninth of a series of such meetings, will be held on the 14th and 15th October 2004 in Heidelberg, Germany, as an adjunct to the 5th International Conference on Systems Biology (ICSB 2004). We seek funding to help defray the costs of holding the SBML meeting and providing travel support for a subset of the attendees. The goals of this meeting include: (1) providing a forum where consensus decisions can be made about the development and adoption of future features of SBML; (2) ensuring that systems biology software interoperability is maximized through the correct use of SBML; and (3) providing a forum for software developers to exchange information about the systems biology software that is available or under development, thereby maximizing the use of that software both directly by users and within other software development projects. The agenda for the SBML Forum will be divided into presentation sessions and discussion sessions. The subject matter of the presentations will include the experiences of software developers using SBML in the field and proposals for mew features in future levels of SBML. Discussions will cover the development of suites of test models to ensure consistent interpretation of SBML and decisions concerning the adoption of feature proposals into the SBML standard. The meeting will attract an eclectic audience representing a variety of disciplines and stages of career development. The forum proceedings will be distributed to attendees and will be made available on the meeting's web site.